Pentylenetetrazole (PTZ) when administered subcutaneously to mice causes various types of seizure activity. First observed is myoclonic jerks, followed by clonic seizures and finally by clonic running and generalized tonic extension seizures. With low doses the initial seizures only are observed. By increasing the dose, the entire seizure complex occurs. The convulsive dose 50 needed to induce clonic seizures in mice without inducing tonic hindlimb extension was found to be 60 mg/kg. The CD50 of PTZ needed to induce the entire seizure complex was found to be 95 mg/kg. Brain concentration of PTZ were measured by gas liquid chromatography following the administration of 60 mg/kg an 95 mg/kg at the time of clonic seizures and tonic hindlimb extension, and were found to be 53 microgram/gm and 79 microgram/gm respectively. There appears to be a relationship between the amount of PTZ in the brain and the severity of seizures induced by PTZ.